In the production of hydrocarbons from marine oil and gas deposits, a fluid communication system from the sea floor to the surface is required. Such a system usually includes multiple conduits through which various fluids flow between a subsea well or pipeline to a surface facility. The multiple conduits for communicating with a surface facility typically include subsea trees, manifolds, production and export flowlines, buoys and riser systems.
One method for producing hydrocarbons from marine oil fields is to use a fixed facility attached to the seafloor, however; fixed facilities can be enormously expensive. A lower cost approach for producing from marine oil fields involves the use of floating facilities or floating vessels. Floating vessels present additional challenges as they can undergo a variety of movements in an offshore environment and are exposed to rapidly changing and unpredictable surface and sub-surface conditions. In particularly extreme weather conditions, it may be necessary for the floating vessel to disconnect from its associated production flowline and riser system.
Common industry practice is to accommodate vessel rotation about a riser system by means of a turret and swivel assembly, which may be internal or external to the floating vessel. The riser system is designed to terminate in a turret buoy, which is designed to interface with a rotatable swivel located on the floating vessel. Such marine riser systems include Submerged Turret Production (STP), and Submerged Turret Loading (STL) to transfer the produced hydrocarbons under high pressure to a production plant or storage unit on a floating vessel. Unfortunately, commercially available and operating production swivels are limited to design pressures of less than 5,000 psig, while well head shut in pressure is capable of reaching over 10,000 psig at the surface.
Given a high reservoir pressure, overpressure of the production swivel and the downstream components poses a substantial risk. Therefore there is a need for a pressure protection system that can be used in conjunction with a swivel and turret buoy to achieve offshore production of hydrocarbons without exceeding the pressure limitation of the production swivel. The aim of the present invention is to provide an alternative in which the above mentioned problems are overcome or in the very least alleviated.
The invention in its preferred embodiments provides an overpressure protection system incorporated in the turret buoy to prevent overpressure of the production swivel and the downstream components. Additionally, locating the pressure protection system in the turret buoy offers easy access, and inexpensive installation, operation and maintenance compared to subsurface locations.